TeslaSCADA reads every poll interval (you setup it in the server setting) only tags that bound to the graphical displayed on the opened screen. Also it reads tags that use alarms (alert variables in you case) and history. If you want to read only alert variables make the screen without tags bound to graphical object (empty screen with call screen buttons). In this case TeslaSCADA will read only variables with check alarms and history settings. If some alert is happened you can call screen you want to discover.